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'G' is one of the beam-target double polarisation observables, arising from a linearly polarised beam with a longitudinally polarised target In this case, terms not involving linear polarisation of the beam and longitudinal polarisation of the target are zero and the above expression becomes a lot simpler:

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The effect of G can be seen by examining the asymmetry distribution for positive and negative longitudinal target polarisations The distributions for the positive (top) and negative (bottom) target polarisations show a phase shift due to change in target polarisation By adding distributions for the two target polarisations, the G contribution can be eliminated and a measurement of can be attempted on Butanol If we take similar asymmetries of Kaon azimuthal angle distributions for the Butanol data, the amplitude of a cos(2) fit is not a pure measurement of the observable – it also contains a contribution from the G observable

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● The A2 Hall is a real photon experimental setup ● It uses a tagged photon beam, which stimulates a reaction within the target cell. A collection of detection systems are then used to measure the reaction products

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● Electrons scattering of a radiator produce bremsstrahlung photons ● Scattered electrons are bent into an electron focal plane via the Tagger dipole magnet ● The position on the focal plane is used to determine the energy of the bremsstrahlung photon incident on the experimental target

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● Electrons scattering of a radiator produce bremsstrahlung photons ● Scattered electrons are bent into an electron focal plane via the Tagger dipole magnet ● The position on the focal plane is used to determine the energy of the bremsstrahlung photon incident on the experimental target

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● Electrons scattering of a radiator produce bremsstrahlung photons ● Scattered electrons are bent into an electron focal plane via the Tagger dipole magnet ● The position on the focal plane is used to determine the energy of the bremsstrahlung photon incident on the experimental target